1. Field of the Invention
The present invention relates to an optical coordinate input apparatus and a position indicator thereof capable of inputting information about manuscripts, figures, precise drawings, and the like to a host apparatus. More particularly, the present invention relates to an optical coordinate input apparatus and a position indicator thereof which can be optionally applied to a subject two-dimensional coordinate plane and in which a region to which indications of coordinates are substantially free from restrictions.
2. Description of Prior Art
There are a variety of so-called coordinate input apparatuses capable of deriving two dimensional coordinates of an object being tracked; exemplary of the mechanisms used in these devices are electrostrictive, electromagnetic induction, pressure and electrostatic induction type. All of these apparatuses basically include a coordinate indicating portion having a tablet (or a keyboard) defining a two dimensional coordinate plane and a movable position indicating apparatus. The tablet and the position indicating apparatus are connected to each other by an electric, magnetic, or mechanical signal so that the position on the two-dimensional coordinate plane of the position indicating apparatus is detected. Thus, the input coordinates are indicated.
However, the above-described conventional coordinate input apparatuses require an exclusive tablet of a special structure having predetermined dimensions, shape, and structure in accordance with the physical mechanism used for enabling the signal transmission/receipt to and from the position indicating apparatus. Therefore, there has been a paper size limit from the viewpoint of the manufacturing technology, the largest paper size being about A0 size even if the electromagnet type apparatus, which is considered to be advantageous in accuracy and to be thereby suitable to larger sizes, is used. Furthermore, the plane region to which input of the coordinates can be provided has been necessarily limited by the area of the tablet. Therefore, input signals representing graphics drawn over an optional area cannot be freely provided regardless of whether the area is wide or narrow.
The position indicators of the above-described conventional coordinate input apparatuses have usually been combined with an exclusive tablet capable of transmitting and receiving a signal. Therefore, the conventional coordinate input apparatuses cannot solely (that is, in a manner separated from the tablet) be applied to an optional two dimensional coordinate plane. Furthermore, since the dimensions of the plane of the exclusive tablet have been physically limited, the position indicator cannot easily derive two dimensional information for a wide area.